Improved admin model registration options: you can now register using…

… register(Model, **options) and even register(Model, ModelAdmin, **options). This isn't documented yet -- a much expanded version of docs/admin.txt is on the way.
git-svn-id: http://code.djangoproject.com/svn/django/trunk@8063 bcc190cf-cafb-0310-a4f2-bffc1f526a37